Roller stamper for molding a substrate sheet to become an information recording medium

ABSTRACT

A roll stamper which molds a substrate resin sheet into an information recording media by continuously transferring preformat patterns on the substrate resin sheet, and a production process therefor. The preformat pattern on the roll stamper has a value of b/a of greater than 1 when the length of the preformat pattern in a direction parallel to the direction in which the resin sheet is transported is defined as a and the length in a direction perpendicular thereto as b.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 07/669,181filed Mar. 13, 1991, now abandoned which application is acontinuation-in-part of application Ser. No. 629,574, filed Dec. 18,1990, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a roll stamper for continuouslyproducing substrates for information recording media by formingpreformats on a resin sheet. It also relates to a process for producingthe roll stamper.

2. Related Background Art

Preformats such as track grooves or address pits are formed onsubstrates for information recording media such as optical disks. As amethod of continuously mass-producing such substrates, Japanese PatentApplication Laid-open No. 56-86721 discloses a method in which athermoplastic synthetic resin sheet is heated and softened using aninfrared lamp and thereafter signals in the form of grooves or pits aretransferred using a molding roll.

The roll stamper used in such a method is prepared by sticking aflat-plate thin stamper on a mirror-finished roll substrate with anadhesive or the like or mechanically fastening the stamper on thesubstrate by means of a jig or the like, or by directly forming apreformat pattern on the body of a roll substrate.

As the preformat pattern formed on the roll stamper is used a preformatpattern similar to those used in conventional methods in which thesubstrate is formed sheet by sheet as in the injection process, thecompression process and the photopolymerization process (hereinafter "2Pprocess"), which pattern is substantially circular, for example, in thecase of a disk.

With regard to the accuracy of the preformat pattern provided on thestamper used in the conventional injection process, compression processor a 2P process, tracking errors tend to occur unless a deviation from acircle is controlled to be not more than 100 μm in the case of the disk.

When preformats are, however, continuously formed on a resin sheet, arelatively large pressure is applied to the roll stamper or shrinkagemay occur with the cooling of resin, in a direction perpendicular to thedirection in which the resin sheet is transported. Hence, in the casewhere the roll stamper on which the above substantially circular patternhas been formed is used, there is the problem that the preformattransferred onto the resin sheet causes a lowering of transfer accuracy,specifically, a lowering of the circularity or roundness. In particular,in the case of recording media like optical disks on which fine patternsare formed and information with a high density is recorded andreproduced, the lowering of the roundness may cause errors such astracking-off.

This is also a problem in the case of molding a substrate for an opticalcard by a roll stamper, particularly resulting in a problem that theoptical card substrate will become a defective product out of thespecification due to the change in track pitch of the preformat patternby shrinkage of the resin sheet, and it has been desired to have acountermeasure against the deformation of the preformat patternaccompanied with shrinkage of the resin sheet, particularly shrinkage ina direction vertical with respect to the conveying direction of thesheet.

SUMMARY OF THE INVENTION

The present invention was made taking account of the above problems. Anobject of the present invention is to provide a roll stamper used formolding a substrate sheet for information recording mediums, that canaccurately form preformats in a continuous manner on a resin sheet, anda process for producing such a stamper.

Another object of the present invention is to provide a process forproducing a substrate sheet for information recording media, that canobtain an information recording medium substrate sheet on whichpreformats have been accurately formed.

The roll stamper of the present invention for molding a substrate sheetfor information recording mediums is a roll stamper which molds asubstrate sheet for information recording mediums by continuouslytransferring preformat patterns on a resin sheet, wherein the preformatpattern on the roll stamper has a value of b/a greater than 1 when thelength of the preformat pattern in a direction parallel to the directionin which the resin sheet is transported is defined as a and the lengthin the direction perpendicular thereto as b.

The process of the present invention for producing a substrate sheet forinformation recording media is a process for producing a substrate sheetfor information recording media, comprising continuously transferringpreformat patterns on a resin sheet by the use of a roll stamper,wherein the preformat pattern on the roll stamper has a value of b/a ofgreater than 1 when the length of the preformat pattern in a directionparallel to the direction in which the resin sheet is transported isdefined as a and the length in the direction perpendicular thereto as b.

The process for producing the roll stamper of the present invention is aprocess for producing a roll stamper which molds a substrate sheet forinformation recording media by continuously transferring preformatpattern on a resin sheet, comprising the steps of;

a) while an original plate having thereon a photoresist layer is rotatedat a given number of revolution, vibrating a cutting head for cutting apattern on the photoresist layer, corresponding to the preformatpattern, or vibrating the original plate, at a frequency twice the givennumber of revolution of the original plate and in the diameter directionof the original plate, thereby cutting the pattern on the photoresistlayer, followed by development to form a resist pattern in which eachtrack is elliptical and which has an elliptical shape having a value ofb/a of greater than 1 when the length of the minor axis is defined as aand the length of the major axis as b, at the outermost track;

b) carrying out electroforming on the resist pattern to form a stamperhaving the preformat pattern; and

c) fixing the stamper to a roll substrate in such a manner that theminor axis direction of said pattern is in accordance with the directionin which the resin sheet is transported.

The roll stamper for molding of the substrate sheet for the informationrecording medium of the present invention is a roll stamper having apreformat pattern corresponding to the preformat of the informationrecording medium, which is used for transferring the preformat patternonto a resin sheet in succession to mold a substrate sheet for aninformation recording medium, characterized in that when a predeterminedlength and width of the preformat of the information recording mediumare defined as A and as B, respectively, the preformat pattern is formedto have a size of a length a corresponding to the above length A in theperipheral direction of the roll stamper and a width b corresponding tothe above width B in a direction vertical with respect to the peripheraldirection, and the value of b/a being greater than the value of B/A.

The roll stamper of the present invention is a roll stamper having apreformat pattern corresponding to the preformat of an informationrecording medium, which is used for transferring the preformat patternonto a resin sheet in succession to mold a substrate sheet for aninformation recording medium, characterized in that a plurality of thepreformat patterns are formed in the peripheral direction of the rollstamper and the preformat pattern, when a predetermined length and widthof the preformat are defined as A and B, respectively, has a size of alength a corresponding to the above length A in the peripheral directionof the roll stamper and a width b corresponding to the above width B ina direction vertical with respect to the peripheral direction, and thevalue of b/a being greater than the value of B/A.

A process for preparing the roll stamper of the present invention is aprocess for preparing a roll stamper for molding of a substrate sheetfor an information recording medium by transferring continuously apreformat pattern onto a resin sheet, having in the peripheral directiona plurality of preformat patterns corresponding to the preformat of aninformation recording medium, comprising the following steps:

a) the step of forming a plurality of preformat patterns correspondingto the preformat of the information recording medium on a lengthy basefilm in the lengthwise direction of the base film to prepare a base filmmaster;

b) the step of forming an electroconducting film on the pattern formedsurface of the base film master;

c) the step of forming a metal film on the electroconducting filmaccording to an electroforming method;

d) the step of preparing a flexible stamper in a continuous lengthhaving a plurality of preformat patterns by peeling theelectroconducting film and the metal film from the base film master;

e) the step of fixing the flexible stamper onto a roll substrate.

A process for preparing a substrate sheet for the information recordingmedium of the present invention is a process for preparing a substratesheet for information recording medium, in which a preformat pattern istransferred successively onto a resin sheet by use of a roll stamperhaving the preformat pattern, characterized in that the preformatpattern, when a predetermined length and width of the preformat isdefined as A and B, respectively, is formed to have a length acorresponding to the above length A in the peripheral direction of theroll stamper and a width b corresponding to the above width B in adirection vertical with respect to the peripheral direction, the valueof b/a being greater than the value of B/A.

A process for preparing a flexible stamper in a continuous lengthcomprises the steps of: preparing a base film master by forming aplurality of preformat patterns corresponding to the preformat of aninformation recording medium on the surface of a base film in acontinuous length in the lengthwise direction of the base film; formingan electroconducting film on the pattern formed surface of the base filmmaster; forming a metal film so as to be integral with theelectroconducting film on the electroconducting film according to anelectroforming method; and peeling the electroconducting film and themetal film from the base film.

A process for preparing a flexible stamper of the present inventioncomprises the steps of: forming an electroconducting film on the surfaceof a base film in a continuous length; forming a metal film on theelectroconducting film according to an electroforming method, andforming a plurality of preformat patterns corresponding to the preformatof the information recording medium on the metal film in the lengthwisedirection of the base film by use of a photo-lithographic process.

Further, the electroforming apparatus of the present invention is anelectroforming apparatus for forming a metal film on a film madeelectroconductive while conveying continuously a base film master madeelectroconductive having a plurality of preformat patterns correspondingto the preformat of an information recording medium on the surface of abase film in a continuous length int he lengthwise direction of the basefilm, and an electroconducting film formed on the preformat patternforming surface of the base film, which comprises means for keepingcontinuous contact with the electroconducting film to electricallyconnect the electroconducting film to a power source.

In this way the size of a preformat pattern is deviated from itsstandard shape in a specific range. It is thus possible to compensatethe deformation of a preformat transferred onto a resin sheet, caused bythe elongation of a stamper that may occur when a preformat istransferred onto a resin sheet and by the shrinkage due to cooling onthe resin sheet, so that a very accurate preformat can be formed on theresin sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates an embodiment of the pattern form ofthe roll stamper according to the present invention.

FIG. 2 diagrammatically illustrates an embodiment of a roll stamper, inwhich the stamper shown in FIG. 1 is fixed on a mirror-finished roll.

FIG. 3 schematically illustrates the process of transferring preformatpatterns on a resin sheet, using the roll stamper according to thepresent invention.

FIG. 4 diagrammatically illustrates an embodiment of the process forproducing a substrate sheet for information recording mediums, using theroll stamper according to the present invention.

FIGS. 5 and 6 are each a schematic cross-sectional view of a cuttingapparatus for a master used for the production of the roll stamperaccording to the present invention.

FIGS. 7A and 7B are schematic illustrations showing flexible stamper ofthe present invention, in which "A" is an optical disc and "B" is anoptical card.

FIG. 8 is a schematic illustration showing another embodiment of theroll stamper of the present invention.

FIGS. 9A and 9B are schematic illustrations showing still anotherembodiment of the roll stamper of the present invention.

FIGS 10A, 10B, 10C and 10D are diagrams of the steps of a preparationmethod of the flexible stamper shown in FIG. 7.

FIGS. 11A, 11B, 11C and 11D are diagrams of the steps of anotherpreparation method of the flexible stamper shown in FIG. 7.

FIGS. 12A, 12B and 12C are diagrams of the steps of still anotherpreparation method of the flexible stamper shown in FIG. 7.

FIG. 13 is a schematic illustration of an electroforming apparatus to beused for preparation of the flexible stamper.

FIGS. 14A, 14B and 14C are schematic illustrations of a current passagemeans of the electroforming apparatus in FIG. 13.

FIGS. 15A, 15B and 15C are views for explanation of the fixing method ofthe flexible stamper onto a roll substrate.

FIGS. 16A, 16B, 16C and 16D are diagrams of the steps of still anotherpreparation method of the flexible stamper shown in FIG. 7.

FIG. 17 is a view for explanation of a predetermined size of thepreformat formed on an optical card substrate.

FIG. 18 is a schematic illustration of the flexible stamper in acontinuous length of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The roll stamper of the present invention for molding a substrate sheetfor information recording mediums will be described below in detail withreference to the drawings.

FIG. 1 diagrammatically illustrates a preformat pattern 11 formed on thestamper of the present invention. In FIG. 1, the letter symbol arepresents the diameter in a direction parallel to the direction inwhich a resin sheet is transported, corresponding to the diameter of theoutermost track of a pattern formed on the stamper. The letter symbol brepresents the diameter of this pattern in the direction perpendicularto the direction in which the resin sheet is transported. The rollstamper of the present invention is characterized in that the value ofb/a (the value of b divided by a) is greater than 1.

FIG. 8 illustrates schematically another roll stamper of the presentinvention, in which a indicates the length in the peripheral directionof the roll stamper of the track at the outermost side of the preformatpattern formed on the stamper, and b indicates the width in thedirection vertical to the roll stamper, and such a and b correspondrespectively to A and B which are the predetermined length and width ofthe preformat of the information recording medium, characterized in thatthe value of b/a is made greater than that of B/A.

In this way a difference is provided in the size ratio between thepreformat pattern formed on the roll stamper and the standard shape ofthe preformat to be transferred to the resin sheet. It is thus possibleto compensate for the deformation of a preformat transferred onto aresin sheet, caused by the elongation of a stamper that may occur whenthe resin sheet and the stamper are brought into contact and by theshrinkage of the resin sheet, so that a preformat can be very accuratelyformed on the resin sheet.

In the roll stamper of the present invention, the relation between a andb should satisfy the following expression (1), and, particularly whenthe preformat is formed on a molten resin sheet, should preferablysatisfy the following expression (2).

    0.05≦(b-1/1)×100≦2                     (1)

    0.1≦(b-a/a)×100≦1                      (2)

Use of the stamper that satisfies the relation represented by the aboveexpression makes it possible to particularly minimize the deformation ofa preformat transferred onto the resin sheet, caused by the elongationof a stamper that may occur when the preformat is transferred onto theresin sheet and by the shrinkage of the resin sheet that may occur afterthe transfer.

There are not particular limitations on the shape and size of thepreformat pattern formed on the roll stamper of the present inventionand patterns with any shape and size can be used so long as theycorrespond to preformats formed on substrates of information recordingmediums.

Grooves or pits formed on a substrate of an optical recording mediumsuch as an optical disk or optical card on which information is recordedor reproduced by means of light are exemplified by tracking grooves inthe form of concentric circles, a spiral or stripes, having a groovewidth of from 0.1 μm to 5 μm, a pitch of from 1 μm to 12 μm and a depthof from 0.01 μm to 0.4 μm, or information pits with a size on the micronorder. A slight elongation or shrinkage in size of such grooves or pitswhich may occur when they are transferred brings about defects in theoptical recording medium. Stated specifically, when, for example, atracking groove for an optical disk is transferred to a resin sheet, anelongation in size on its outer diameter produces an eccentricity in theoptical disk to cause tracking errors, making it impossible to carry outrecording and reproducing. Accordingly, in the case of a disk pattern,the deviation of the size on its outer diameter from a circle shouldpreferably be not more than 90 μm, particularly not more than 50 μm, andmore particularly not more than 30 μm.

Thus the roll stamper of the present invention is capable of accuratelytransferring such fine patterns on a resin sheet, and is particularlyeffective for the production of substrates for optical recording mediumssuch as optical disks and optical cards.

As an example for the process for producing the roll stamper of thepresent invention, a photoresist layer is formed on a glass plate for amaster and a pattern is drawn using a laser beam or electron beam, whichis then developed to form a resist pattern. The resist pattern issubjected to Ni-electroforming, thereby to give a thin Ni stamper. Next,as shown in FIG. 2, this Ni stamper 21 is fixed to a mirror-finishedroll substrate 22 by using an adhesive or a jig. A roll stamper can bethus obtained. Alternatively, a preformat pattern may be formed directlyon the roll substrate or on a pattern forming layer provided on thesubstrate.

Here, the value of b/a of the preformat pattern on the stamper can beset to a given value in the following manner. For example, in the caseof an optical disk, the pattern of tracking grooves is prepared in acircular form, and the stamper thus prepared is stretched by applying atension thereto in the direction perpendicular to the direction in whicha resin sheet is transported. The resulting stamper is fixed to the rollsubstrate. The roll stamper of the present invention can be thusobtained.

In the case of a roll stamper for molding a substrate sheet for opticaldisks, the roll stamper can be produced in the following manner: In thestep of producing the the above Ni stamper, when a photoresist layer isformed on the glass plate for a master and a pattern is drawn on thisresist layer by irradiation with a laser beam or the like, an opticalhead for carrying out irradiation with the laser beam while the glassplate for a master is rotated (hereinafter "cutting head") is vibratedin the diameter direction of the glass plate for a master at a frequencytwice the number of revolution of the glass plate. An elliptical patterncan thereby be drawn and at the same time the difference between themajor axis and the minor axis of this elliptical form can be made equalto the amplitude of vibration of the cutting head. Then, the Ni stamperobtained by Ni-electroforming using this glass plate may be fixed to theroll substrate in the manner that the direction of the minor axis of theelliptical pattern is in accordance with the direction in which a resinsheet is transported. Thus the roll stamper of the present invention formolding the substrate sheet for information recording medium can beproduced. In this instance, a stamper having an elliptical pattern canbe obtained without applying any tension to the stamper, and hence it ispossible to prevent the stamper from being broken.

FIG. 5 illustrates an embodiment of a drawing apparatus for the masterused in the production of this roll stamper.

In FIG. 5, the numeral 51 denotes a laser oscillator. A non-modulatedlaser beam is outputted from the laser oscillator 51. The numeral 53denotes a modulated signal generator. A modulated signal correspondingto a pattern to be cut on a resist layer formed on an original plate 56,to be described later, for a master used for the stamper is outputtedfrom the modulated signal generator 53. The numeral 52 denotes anoptical modulator. In the optical modulator 52, the laser beam outputtedfrom the above laser oscillator 51 is modulated corresponding to themodulated signal outputted from the above modulated signal generator 53,and the modulated laser beam is fed to a cutting head 54. Through thecutting head 54, the laser beam having been modulated though the opticalmodulator 53 is made to vertically downwards converge on the surface ofa resist layer on the original plate 56, made of glass, for a masterused for the stamper (hereinafter "glass original plate 56") which isplaced on a turn table 57. The cutting head is supported in the mannerthat it is slidable in the diameter direction of the glass originalplate 56 by means of a horizontally sliding mechanism (not shown), and apiezoelectric device 60 is provided between the side of the abovecutting head 54 and a machine frame 61. The piezoelectric device 60expands or contracts according to an alternating voltage applied from acontrol means (not shown) and hence can reciprocate the above cuttinghead 54 in the diameter direction of the glass original plate 56.

The glass original plate 56 is provided on its surface with a resistlayer 55. A pattern is cut on the resist layer 55 by means of the laserbeam made to converge through the cutting head. Beneath the turn table57, a motor 59 for direct drive is fitted, the number of revolution ofwhich can be precisely controlled by the operation of the above controlmeans and the turn table 57 can be rotated the turn table 57 around aspindle 62. The motor 59 is supported by a horizontally slidingmechanism 58 in the manner that it is slidable in the right-and-leftdirection shown in the drawing, and also is equipped with a feedmechanism (not shown) so that it can be slided to a given position bythe operation of the above control means. The control means gives acommand to the modulated signal generator 53 to cause a modulated signalto be outputted at a given speed. In accordance with the speed, it alsocontrols the number of revolution of the motor 59, the frequency ofvibration of the piezoelectric device 60 and the position of the cuttinghead 54 and changes the amplitude of vibration of the piezoelectricdevice 60 in accordance with the position of the cutting head 54.

The process for producing the roll stamper according to the presentinvention will be described below with reference to FIG. 5.

The motor 59 is rotated at a predetermined number of revolution underthe control by the control means (not shown), and thus the turn table 57and the glass original plate 56 are rotated by the rotation of the motor59. In this state, the feed mechanism (not shown) is driven so that themotor 59, the turntable 57 and the glass original plate 56 are slidedusing the slide mechanism 58 to effect alignment. A laser beam and amodulated signal are then outputted from the laser oscillator 51 and themodulated signal generator 53, respectively, which are modulated in theoptical modulator 52 and a modulated laser beam is outputted to thecutting head. Then the modulated laser beam is shot onto the resistlayer 55 on the surface of the glass original plate 56 and thus thecutting head 54 cuts the resist layer to form a pattern corresponding tothe modulated signal. At this time, the control means described above isoperated to cause the piezoelectric device 60 to vibrate in the diameterdirection of the glass original plate 56 synchronizing with therevolution of the motor 54, thereby causing the cutting head 54 tovibrate at a frequency twice the number of revolution of the motor 59.

Here, the amplitude of vibration given to the cutting head 54 may be setin accordance with the value of b/a of the preformat pattern to beformed on the roll stamper.

This amplitude of vibration may also be controlled as a function of thedistance Q between the center of the glass original plate 56 (or thespindle 62 of the turn table 57) and a laser beam spot on the resistlayer 55; in other words, the amplitude of variation may be made to varyfor each track. This is preferred since the elliptical tracking grooveor grooves having a constant ratio between the major axis and the minoraxis can be formed over the whole track or tracks. As a proportionalfactor of the distance Q, the factor may also be determined inaccordance with the material for a disk substrate, the speed of molding,etc. so that the preformat pattern can be more rounded on a resin sheet.In particular, when this proportional factor is set to range from 0.001to 0.04, particularly from 0.002 to 0.02, the tracking grooves for adisk substrate can be accurately formed on a resin sheet.

The cutting head may not be vibrated and instead the original master 56may be vibrated as shown in FIG. 6.

After the cutting for one track is completed in this way, the motor 59,the turntable 57 and the glass original plate 56 are slided for onepitch (step feed) in the same way as int he above alignment, and thenthe pattern is cut on the resist layer formed on the glass originalplate 56, in the same way as in the cutting described above. Thisoperation is successively repeated to cut the resist layer on the glassoriginal plate 56 to form thereon a preformat pattern for a disk. Aresist pattern obtained by developing the resist layer is subjected toknown steps such as post-baking, nickel sputtering, nickelelectroforming, back polishing and external finishing. thus a stamperhaving the preformat pattern 11 as shown in FIG. 1 can be obtained.

In FIG. 1, the letter symbol a represents the length of the minor axisof the outermost track; and b, the length of the major axis of the sametrack. The stamper having this preformat pattern is fixed to the rollsubstrate 22 in the manner that the direction of the minor axis of theabove pattern may be in accordance with the direction in which a resinsheet is transported. Thus the roll stamper of the present invention formolding a substrate sheet for optical disks can be obtained.

In the above method of making the master, the amplitude of variation inthe above vibration may be made substantially constant when thepreformat pattern may not be in an excessively flat elliptical form andalso it is unnecessary for the ratio of the major axis to the minor axisto be strictly equal over the whole track or tracks. In such aninstance, it becomes unnecessary to provide the means for changing theamplitude of variation in proportion to the distance Q between thecutting head 54 and the center of the glass original plate 56, so thatthe cost can be lowered.

In the present invention, metals, semiconductors, dielectrics or alloysmay be used as materials for the roll substrate. For example, aluminum,glass, hard metal, mold steel (e.g. maraging steel) may be used, whichare materials feasible for mirror-finishing. Particularly preferred isCr steel, which can be mirror-finished with ease.

In the present invention, as shown in FIG. 7, a stamper 116 having aplurality of preformat patterns 11 arranged in the peripheral directionof the roll substrate can be used as the flexible stamper to be fixed onthe roll substrate surface. When a roll stamper as shown in FIG. 8 isformed by use of such stamper, because unevenness on the surface of theroll stamper can be reduced to great extent as compared with the rollstamper as shown in FIG. 9 comprising one performat pattern of theinformation recording medium formed on one flexible stamper and having aplurality of flexible stampers fixed on the peripheral surface of theroll substrate, a substrate sheet for a recording medium producing goodsurface state can be obtained, whereby an information recording mediumwith little noise can be prepared.

Such a flexible stamper having a plurality of preformat patterns 11 isformed by sputtering an electroconducting film 114 onto a glass master101 having a plurality of resist patterns 102 corresponding to thepreformat pattern of an information recording medium having thepredetermined size of a and b according to the method described above asshown in FIG. 10, then forming a metal film 115 to integrate theelectroconducting films with the metal films and peeling the integratedfilms from the glass master to obtain a flexible stamper 116 having aplurality of preformat patterns 11.

By fixing the flexible stamper on the roll substrate 22 by means of afixing implement shown in FIG. 15 or screwing, etc., it becomes possibleto easily exchange the stamper, and yet a roll stamper which can beprepared inexpensively can be obtained.

Also, using the flexible stamper prepared above as the father stamper,coating and curing a UV-ray curable resin on the flexible stamper toprepare a mother stamper made of a resin and forming anelectroconducting film and a metal film on the stamper, followed bypeel-off, whereby the flexible stamper of the present invention, can beobtained. Further, the above-mentioned mother stamper can be alsoprepared by a casting method.

Further, using a base film master 113 comprising a plurality of resistpatterns corresponding to preformat patterns formed on the base film 111as shown in FIG. 1 in place of the glass master having a plurality ofpreformat patterns when the above-mentioned flexible stamper isprepared, an electroconducting film 114 is formed on the pattern formedsurfaces of the base film master, and subsequently a metal film 115 isformed by electroforming, so that a flexible stamper 116 having aplurality of preformat patterns 11 can be also obtained. In this case,the use of a film (base film) as the substrate for preparing the stamperenables a base film master having electroconducting films formed thereonto be wound up in a roll, and it becomes possible to apply continuouslyan electroforming treatment while delivering it out from the roll, ifdesired.

It is also possible to directly form preformat patterns 11 on the basefilm 111 as shown in FIG. 12 to form a base master 113, therebyobtaining a flexible stamper 116.

Next, the method of performing continuous electroforming treatment byuse of a base film master is described.

FIG. 13 is a schematic sectional view of an electroforming apparatus forcarrying out continuously electroforming treatment by delivering a basefilm master 131 having an electroconducting film 114 wound up in a roll.In the same Figure, 132 denotes a metal chip 133 of nickel, etc. and 134denotes a delivery roller and also a current passage means for providinga current passage between the electroconducting film 114 and the powersource 135. As shown in FIG. 13, the nickel chip in the electroformingtank 136 and the electroconducting film 114 formed on the surface of thebase film master are set on the + side and the - side electrode,respectively, and the base film master 131 is delivered continuouslyinto the electroforming solution.

In this device, an enlarged view for the roll 133 which is the currentpassage means, is shown in FIG. 14. FIG. 14A is a side view of the rolland FIG. 14B a front view. Here, the rolls 133, 134 are each constitutedso as to sandwich the base film master 131 between the rolls 133-1 and133-2, and the roll 133-2 maintains continuously the contact state withthe electroconducting film 114 of the base film master, with its contactportion comprising at least an electroconductive material connected to apower source. The present embodiment, as shown in FIG. 14B, is adaptedto have the both ends of the roll 134-1 as the electroconductiveportions 134-1a and the small diameter portion positioned therebetweenas the non-electroconductive portion 134-1b.

In the present invention, the means to electrically connect theelectroconducting film 114 to the power source 135, is not limited tothe above-mentioned roll-shaped one, provided that continuous contactstate with the electroconducting film can be maintained and conductionwith the power source can be stably obtained. For example, as shown inFIG. 14C, the means comprising an electroconductive member 137 having apressing means 136 such as a spring, etc. can be used.

In either case, the current passage sites may be only at the both endsof the base film master. The use of such a means eliminates therestriction in the lengthwise direction of the base film master, so thatthe length of the flexible stamper can be freely set corresponding tothe sizes of the roll substrate and the preformat pattern.

While conveying the base film master, a nickel metal film of 100 to 200μm is deposited under the electrolytic conditions of a time integratedvalue of the current flowed of 17 to 34 A·H (ampere·hour), subsequentlythe electroconducting film 114 and the metal film 115 in one body arepeeled from the base film master, and the photoresist attached on thesurface is removed, and as a result a flexible stamper 116 having adesired number of preformat patterns can be obtained.

Finally, as shown in FIGS. 15A and 15B, the flexible stamper 116 isfixed between the roll substrate 22 and the stamper fixing implement 153as shown in FIGS. 15A and 15B with the stamper fixing implement fixingonto the roll substrate with a screw, thereby fixing one to pluralsheets of flexible stampers having a plurality of preformat patternsaround the peripheral surface of the roll substrate on the peripheralsurface of the roll substrate, so that the roll stamper of the presentinvention can be obtained.

Also as shown in FIG. 15C, both ends of the flexible stamper 116 can befixed with the stamper fixing implement and the screw to obtain the rollstamper of the present invention.

As the base film to be used in the preparation of the stamper describedabove, any one which can stand various conditions in an electroformingsolution, for example, on excellent in acid resistance (pH 3 to 4) andheat resistance (50 to 70° C.) may be employed. For example, a polyesterfilm is preferably used. The surface roughness of the base film shouldbe desirable 50 to 100 Å.

Another embodiment of the preparation method of the flexible stamper 116by use of the base film is described.

First, an electroconducting film 114 is formed on the base film 111 bysputtering, etc. and then a metal film 115 is formed according to theelectroforming method, followed by polishing of the surface of a metalfilm.

As the polishing method, at least one of drying polishing or wetpolishing is performed to preferably make the surface precision within±3 Newton rings and the surface roughness 50 to 100 Å.

Next, according to the photolithographic steps, a plurality of resistpatterns 161 corresponding to the preformat patterns for a plurality ofinformation recording medium are formed, and then the metal film 115 isetched, whereby a flexible stamper 116 having a plurality of preformatpatterns can be obtained.

Etching may be practiced according to an etching method such as dryetching, wet etching, etc.

In dry etching, for example, a metal film having a resist pattern formedthereon (electroformed file+electroconducting film+base film) can beetched with a reactive gas of C₂ F₆ by means of a dry etching apparatusin which the metal film can rotate on its own axis, and equipped with anion gun for etching. In wet etching, for example, while rotating themetal film (electroplated film+electroconducting film+base film) on itsown axis, etching is effected with a solution of hydrofluoric acid andfluorinated ammonia NH₄ F (1:7 weight ratio) for a time of about 1minute.

After etching, O₂ plasma ashing is applied by use of O₂ to remove theresidual resist and a fine pattern corresponding to the patterningpattern is formed on the metal film.

The flexible stamper 116 thus prepared is fixed on the roll substrate soas to be in contact with the peripheral surface of the roll substrate toobtain the roll stamper of the present invention.

An adhesive was coated on one surface of the base film, and a protectivesheet was covered on the adhesive layer formed. Then, on the surfaceopposite to the side to the adhesive layer of the base film, the aboverespective steps may be also performed to form a plurality of preformatpatterns.

The flexible stamper with one surface being an adhesion surface andhaving a plurality of predetermined patterns of the upper recordingmedium formed on the other surface can be also adhered directly onto aroll substrate to prepare a roll stamper.

Here, the adhesive is not particularly limited, but there can begenerally used natural rubber, styrene-butadiene rubber, regeneratedrubber, butyl rubber, butadiene-acrylonitrile rubber, polyacrylate andpolyvinyl alkyl ether, etc. as the base polymer. Particularly,polyacrylates, etc. having excellent water resistance, heat resistancecan be preferably employed. Also, double-coated tape, etc. may be alsoused as the adhesive. The protective sheet is not particularly limited,but any suitable one may be used in view of water resistance, heatresistance.

When a flexible stamper in a continuous length is thus prepared by useof a base film, when the size of external shape of the preformat of agiven information recording medium is made A (length)×B (width) and thesize of the preformat pattern to be formed on the flexible stamper madea (length)×b (width) corresponding to A, B as mentioned above, it ispreferably formed to be b/a>B/A. By fixing the flexible stamper on theroll substrate so that the length (a) direction of the preformat patternand the peripheral direction of the roll substrate may be consistentwith each other, a roll stamper which can prevent distortion of thepreformat by shrinkage of the resin sheet during extrusion molding canbe obtained.

The present invention is also effective in the case where preparing asubstrate sheet for an optical card as shown in FIG. 7B. Particularly,as the preformat for an optical card, for example, as the track groove171, one shaped in stripe with a groove width of 2.5 μm and a pitch 12μm may be formed, and the track pitch 172 is determined by the standardto suppress its fluctuation within the range of 12 μm±0.1 μm, and if itis outside of this range, a tracking error of recording and reproductionlight is liable to occur. Accordingly, on molding a preformat for anoptical card with a square shape of A×B size as show in FIG. 17 byextrusion molding, when the length of the roll stamper in the peripheraldirection and the length in the direction perpendicular to theperipheral direction are defined as a and b for the lengthscorresponding to the above-mentioned A and B, so that the value of b/ais made greater than that of B/A, the dimensions of the preformatpatterns due to shrinkage accompanied with cooling of the resin sheetsubjected to extrusion molding and transfer of the preformats can becorrected, whereby bulk production of substrates for an optical card ofhigh quality with little tracking error is rendered possible.

Further, when the present invention is applied to the roll stamper foran optical card, and the relationships between A and a and between B andb are made as shown by the formulae (3) and (4), and the length andwidth of the preformat formed on the resin sheet is made a' and b',respectively, the values of a' and b' can be more approximated to A andB, whereby a rolls tamper capable of forming an accurate preformat canbe obtained.

    0.05≦100(a-A)/A≦0.15                         (3)

    0.1≦100(b-B)/B≦0.5                           (4)

Concerning B and b, particularly the relationship represented by thefollowing formula (5) is preferred:

    0.2≦100(b-B)/B≦0.4                           (5).

The process for producing a substrate sheet for information recordingmedia, using the roll stamper of the present invention, will bedescribed below with reference to FIG. 4. FIG. 4 diagrammaticallyillustrates an embodiment of the process for producing a substrate sheetfor information recording mediums according to the present invention.

In FIG. 4, the numeral 45 denotes an extruder for carrying outextrusion; 46, a T-die; and 49, a pressure molding section, comprised ofthree rolls 41, 42 and 43.

At least one roll of these rolls serves as the roll stamper of thepresent invention. In the embodiment shown in FIG. 4, the roll 42 servesas the roll stamper, and the rolls 41 and 43 as mirror rolls.

First, resin pellets 44 put into the extruder 45 are heated and meltedin the barrel of the extruder, pressed forward by a screw, and thenformed into sheet through the T-die. The temperature of the resin atthis time may be in the range of from 260° C. to 330° C., and preferablyfrom 280° to 320° C., in the case of, for example, a polycarbonateresin. From the T-die, the resin is continuously extruded in the form ofa transparent molten resin sheet 47. The T-die is disposed in the mannerthat this molten resin sheet is extruded between the rolls 41 and 42 inthe pressure molding section 49. The space between the tip of the T-dieand the rolls 41 and 42 may preferably be set to be not more than 100 mmso that the resin can be prevented from being cured before it comes intocontact with the rolls. The atmosphere that surrounds the T-die and therolls may preferably be heated to a temperature of 60° C. or more.

Next, the resin sheet extruded between the rolls 41 and 42 is heldbetween the heated roll 42 serving as the roll stamper and the roll 43serving as a press roll, at which a preformat is transferred to theresin sheet.

The roll stamper of the present invention is kept at such a temperaturethat the resin used may not be cured on the rolls.

More specifically, the roll stamper may preferably be heated to atemperature within the range of +20° C. to -20° C. of the temperature atwhich the resin used is thermally deformed. When, for example, apolycarbonate resin is used, the roll stamper may preferably be heatedto have a surface temperature of from 120° C. to 160° C. Namely, whenthe temperature is controlled in the above range, the molten resin sheetis not rapidly cooled and hence no strain due to shrinkage or the liketends to be produced in the resin sheet. The temperature of the pressroll 43 in the pressure molding section may preferably be set to be thesame as or a little lower than that of the roll stamper 42.

The temperature of these rolls can be controlled, for example, byelectrically heating them using a heater casted in the roll or bycirculating a heating medium at the center of the roll.

Next, the resin sheet 47' on which preformats have been formed istransported to take-off rolls 48. The take-off rolls 48 are rollsimportant to the continuous molding of the preformats, and are drivensynchronously with the rolls in the pressure molding section 49. Inother words, these two sets of rolls have the same peripheral speed, andare preferably constructed in the manner that no stress due to a stretchor the like may act on the resin sheet between them. Taking suchconstruction makes it possible to prevent an optical anisotropy frombeing produced at the interior of the resin sheet.

The thickness of the substrate sheet 47' for optical recording mediadepends on the gap or space between the rolls in the pressure moldingsection 49, the divergence between lips of the T-die, and the drawdownthat is governed by the ratio of extrusion speed to stress rate, i.e.,the degree of a stretch.

The sheet thickness is commonly controlled by making the divergencebetween lips of the T-die greater by 20 to 200% than the desired sheetpressure so that the drawdown is increased. In the present invention,however, the drawdown should be controlled to be from 50 to 150° inorder to prevent the optical anisotropy or sheet thickness unevenesscaused by a strain ascribable to drawdown.

Another manufacturing method of the present invention also provides asubstrate sheet for information recording media having accuratepreformats by heating and softening a resin sheet previously formed andthen pressing the roll stamper of the present invention against it totransfer the preformat.

As described above, the roll stamper of the present invention and theprocess for producing a substrate sheet for information recording mediaby the use of the roll stamper make it possible to accurately transferpreformats onto a resin sheet.

It has also become possible to continuously produce a resin sheet onwhich preformats have been accurately transferred.

Further, according to the present invention in which a stamper having aplurality of preformat patterns on one sheet of flexible stamper is usedas the roll stamper, the unevenness of the roll stamper surface can bereduced to great extent, and also the number of the fixing implements ofthe stamper can be made smaller, and a substrate for informationrecording medium with good surface state can be obtained.

Further, molding of a substrate for information recording medium by useof the roll stamper of the present invention enable the production costof the substrate for information recording medium to be lowered toprovide an inexpensive information recording medium.

Also, according to the preparation process and the electroformingapparatus of the flexible stamper of the present invention, a stamper ina continuous length having a plurality of preformat patterns can beprepared with ease, whereby the production cost of the roll stamper canbe lowered to great extent.

EXAMPLES

The present invention will be described below in greater detail bygiving Examples.

Example 1

Using the apparatus as shown in FIG. 5, cutting was carried out on aglass original plate having thereon a photoresist layer, at the partdefined by the distance Q of from 21 mm to 44.5 mm from the center ofthe glass original plate while the glass original plate was rotated at900 rpm. At this time an alternating voltage of 900/60×2=30 Hz wasapplied to the piezoelectric device to cause the cutting head to vibratein the diameter direction of the glass original plate. The amplitude ofvariation at this time was varied to be 0.0039×Q (mm) in accordance withthe distance Q between the cutting head and the center of the glassoriginal plate. The feed speed of the motor, the turntable and the glassoriginal plate was set to be 24 μm/s.

After the cutting was carried out in this way, development was carriedout to give a resist pattern in a spiral form with an elliptical shapeof 89.000 mm in length (a) of the minor axis and 89.174 mm in length (b)of the major axis, corresponding to a tracking groove having, at aconvex part, a width of 0.6 μm and a height of 1,000 Å. Next, thisresist pattern was subjected to Ni electroforming to prepare a stamper.The resulting stamper was adhered with an adhesive (trade name: SO-55;available from Sony Chemicals K.K.) to a roll substrate in the mannerthat the direction of the minor axis of the stamper was in accordancewith the direction in which a resin sheet is transported. A roll stamperwas thus produced.

Using this roll stamper, the apparatus for producing a substrate sheetfor optical recording mediums, as shown in FIG. 4, was set up. In themanner as shown in FIG. 4, the substrate sheet for optical recordingmediums was prepared using an extruder having an screw of 35 mm indiameter and a coat hanger type T-die of 20 cm in width, downwardsprovided to the body of the extruder.

A polycarbonate resin (trade name: Panlite L-1250; available from TeijinChemicals Ltd.) was used as the resin. The pressure molding section 49was comprised of the rolls 41 and 43 serving as mirror rolls, and theroll 42 serving as the roll stamper previously prepared.

The resin sheet was extruded under conditions of extruder barreltemperatures of 300° C. at the part a (Ta), 300° C. at the part b (Tb)and 320° C. at the part c (Tc) of the extruder 45 and a T-dietemperature Td of 320° C., under which a molten resin sheet was formed.At this time the resin temperature was in the range of 280° C. to 330°C.

The roll stamper 42 was kept at a temperature of 140° C. The roll 41 waskept at a temperature lower than that of the roll 42 by 1 to 2° C., andthe roll 43 was kept at a temperature higher than that of the roll 32 by20 to 21° C.

The space between the lips of the T-die and the pressure molding sectionwas set to be 50 mm, and it was surrounded with a heating box to performcontrol so that the atmosphere from the extrusion of the resin to thepressure molding section was kept at 60° C. or higher. The divergencebetween the lips of the T-die was set to 0.48 mm and the gap between therolls 41 and 42 in the pressure molding sections was set to 1.2 mm,under the conditions of which the preformat pattern of the roll stamper42 was transferred to the resin sheet to carry out the production of asubstrate sheet for optical recording media with a thickness of 1.2 mm.

The resin sheet was molded at a speed of 2 m/min. With respect to thepreformats thus formed on the substrate sheet for inforamtion recordingmedia, thus formed, the length of the preformat in the directionparallel to the direction in which the resin sheet was transported wasrepresented by a' and the length in the direction perpendicular theretoby b' as shown in FIG. 3. The lengths a' and b' were measured and thedeviation of b' when viewed on the basis of a' was regarded as theamount of deviation from a circle. This measurement was made on threesamples selected at random. Results obtained are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                              Amount of Amount of amplitude                           Sample                                                                              a'      b'      deviation from                                                                          of tracking error                             No.   (mm)    (mm)    circle (μm)                                                                          signals                                       ______________________________________                                        1     88.689  88.684  5         AA                                            2     88.687  88.683  4         AA                                            3     88.689  88.685  4         AA                                            ______________________________________                                    

Subsequently, substrates were cut out from the substrate sheet foroptical recording media on which the above measurement was made.Thereafter, aluminum was deposited in a thickness of 1,000 Å to produceoptical disks.

The resulting optical disks were evaluated using an optical diskevaluation apparatus (trade name: OMS-1000 Type III; manufactured byNakamichi K.K.) by measuring the amplitude of the tracking errorsignals. The case in which the amplitude at this time was less than 0.2V was evaluated as "AA", the case of from 0.2 V to less than 0.4 V as"A", the case of from 0.4 V to less than 1.0 V as "B", and the case of1.0 V or more up to tracking-off as "C".

Example 2

Using the same apparatus as used in Example 1, cutting was carried outon a glass original plate having thereon a photoresist layer, at thepart defined by the distance Q of from 20 mm to 44.5 mm from the centerof the glass original plate while the glass original plate was rotatedat 1,200 rpm. At this time an alternating voltage of 1,200/60×2=40 Hzwas applied to the piezoelectric device to cause the cutting head tovibrate in the diameter direction of the glass original plate while theamplitude of variation was varied to be 0.0118×Q (mm) in accordance withthe distance Q between the cutting head and the center of the glassoriginal plate.

In this way, a resist pattern was obtained in a spiral form with anelliptical shape of 89.000 mm in length (a) of the minor axis and 89.525mm in length (b) of the major axis, corresponding to a tracking groovefor an optical disk. Next, this resist pattern was subjected to Nielectroforming to prepare a stamper. The resulting stamper was adheredwith an adhesive to a roll substrate in the manner that the direction ofthe minor axis of the stamper was in accordance with the direction inwhich a resin sheet is transported. A roll stamper was thus produced.Subsequently, using this roll stamper, the substrate sheet for opticaldisks was prepared in the same manner as in Example 1 by continuouslytransferring optical disk preformats onto the resin sheet formed byextrusion.

With respect to the preformats thus obtained on the substrate sheet forinformation recording mediums, the amount of deviation from a circle wasmeasured in the same manner as in Example 1. this substrate sheet toproduce optical disks, and the amplitude of tracking error signals wasmeasured. Results obtained are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                              Amount of Amount of amplitude                           Sample                                                                              a'      b'      deviation from                                                                          of tracking error                             No.   (mm)    (mm)    circle (μm)                                                                          signals                                       ______________________________________                                        1     88.733  88.764  31        AA                                            2     88.732  88.761  29        AA                                            3     88.729  88.761  32        AA                                            ______________________________________                                    

Example 3

In the same manner as in Example 1, the roll stamper of the presentinvention was prepared and preformats for optical disks were transferredto the resin sheet formed by extrusion. In the present Example, thepreformat pattern on the roll stamper was in an elliptical shape of89.423 mm in length (a) in the direction parallel to the direction inwhich the resin sheet is transported and 89.793 in length (b) in thedirection perpendicular to the direction in which the resin sheet istransported, and so formed as to correspond to tracking grooves having,at a convex part, a width at the land, of 0.6 μm, a pitch of 1.6 μm anda height of 1,000 Å.

With respect to the preformats thus obtained on the substrate sheet forinformation recording media, measurement was made in the same manner asin Example 1. On optical disks prepared from the substrate sheet, theamplitude of tracking error signals was also measured. Results obtainedare shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                              Amount of Amount of amplitude                           Sample                                                                              a'      b'      deviation from                                                                          of tracking error                             No.   (mm)    (mm)    circle (μm)                                                                          signals                                       ______________________________________                                        1     88.996  88.992  4         AA                                            2     88.995  89.001  6         AA                                            3     89.000  88.995  5         AA                                            ______________________________________                                    

Example 4

A substrate sheet for optical disks was continuously formed in the samemanner as in Example 1 except that the preformat pattern formed on theroll stamper was made to be 89.023 in length (a) and 89.793 in length(b).

With respect to the thus formed preformats of the substrate sheet foroptical disks, thus formed, measurement and evaluation were made in thesame manner as in Example 1. Results obtained are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                                              Amount of Amount of amplitude                           Sample                                                                              a'      b'      deviation from                                                                          of tracking error                             No.   (mm)    (mm)    circle (μm)                                                                          signals                                       ______________________________________                                        1     89.029  89.003  26        A                                             2     89.021  88.989  32        A                                             3     89.032  89.011  21        AA                                            ______________________________________                                    

Examples 5 to 6

Substrate sheets for optical disks were continuously formed in the samemanner as in Example 1 except that the preformat patterns formed on theroll stampers were made to have the lengths a and b as shown in thefollowing Table 5. With respect to the preformats formed on thesubstrate sheet for optical disks, measurement and evaluation were madein the same manner as in Example 1.

Reference Examples 1 and 2

Substrates for optical disks were prepared in the same manner as inExample 1 except that the preformat patterns formed on the roll stamperswere made to have the lengths a and b as shown in Table 5. With respectto the preformats formed on the substrate sheet for optical disks,measurement of size and an evaluation were made.

Results of Examples 5 to 8 and Reference Example 1 and 2 are shown inTable 5.

                                      TABLE 5                                     __________________________________________________________________________              Preformat pattern                                                                         Preformat on                                                                          Amount of                                                                           Amount of                                           on stamper                                                                             Sam-                                                                             resin sheet                                                                           deviation                                                                           ampltitude of                                       a    b   ple                                                                              a'  b'  from circle                                                                         tracking error                                      (mm) (mm)                                                                              No.                                                                              (mm)                                                                              (mm)                                                                              (μm)                                                                             signals                                   __________________________________________________________________________    Example:                                                                      5         89.752                                                                             89.797                                                                            1  89.046                                                                            89.005                                                                            41    A                                         (b - a/a) × 100 =                                                                          2  89.056                                                                            89.011                                                                            45    A                                         0.05               3  89.051                                                                            89.008                                                                            43    A                                         6         89.685                                                                             89.775                                                                            1  89.001                                                                            89.004                                                                             3    AA                                        (0.1)              2  88.999                                                                            89.003                                                                             4    AA                                                           3  89.001                                                                            89.003                                                                             2    AA                                        7         88.981                                                                             89.880                                                                            1  88.980                                                                            89.002                                                                            22    AA                                        (1)                2  88.979                                                                            88.999                                                                            20    AA                                                           3  88.983                                                                            89.004                                                                            21    AA                                        8         88.192                                                                             89.956                                                                            1  88.989                                                                            89.085                                                                            96    B                                         (2)                2  88.988                                                                            89.086                                                                            98    B                                                            3  88.992                                                                            89.081                                                                            89    A                                         Reference Example:                                                            1         89.783                                                                             89.792                                                                            1  89.174                                                                            88.994                                                                            180   C                                         (0.01)             2  89.179                                                                            89.003                                                                            176   C                                                            3  89.172                                                                            88.989                                                                            183   C                                         2         87.518                                                                             90.225                                                                            1  88.906                                                                            89.094                                                                            188   C                                         (3)                2  88.902                                                                            89.090                                                                            188   C                                                            3  88.903                                                                            89.094                                                                            191   C                                         __________________________________________________________________________

Example 7

Using the apparatus as shown in FIG. 6, cutting was carried out on aglass original plate having thereon a photoresist layer, at the partdefined by the distance Q of from 20 mm to 44.5 mm from the center ofthe glass original plate while the glass original plate was rotated at900 rpm. At this time an alternating voltage of 900/60×2=30 Hz wasapplied to the piezoelectric device to cause the motor, the turntableand the glass original plate to vibrate in the right-and-left direction.The amplitude of variation at this time was varied to be 0.0042×Q (mm)in accordance with the distance Q between the cutting head and thecenter of the glass original plate.

After the cutting was carried out in this way, development was carriedout to give a resist pattern in a spiral form with an elliptical shapeof 89.000 mm in length (a) of the minor axis and 89.187 mm in length (b)of the major axis, corresponding to a tracking groove having, at aconvex part, a width of 0.6 μm, a pitch of 1.6 μm and a height of 1,000Å. Next, this resist pattern was subjected to Ni electroforming toprepare stamper. The resulting stamper was adhered with an adhesive(trade name: SC-55; available from Sony Chemicals K.K.) to a rollsubstrate in the manner that the direction of the minor axis of thestamper was in accordance with the direction in which a resin sheet istransported. A roll stamper was thus produced.

Using this roll stamper, a plurality of preformats for optical diskswere transferred onto a polycarbonate resin sheet formed by extrusion,in the same manner as in Example 1. A substrate sheet for optical diskswas thus produced. With respect to the preformats on this substratesheet, measurement and evaluation were made in the same manner as inExample 1.

Example 8

Using the same apparatus as used in Example 9, cutting was carried outon a glass original plate having thereon a photoresist layer, at thepart defined by the distance Q of from 20 mm to 44.5 mm from the centerof the glass original plate while the glass original plate was rotatedat 600 rpm. At this time an alternating voltage of 600/60×2=20 Hz wasapplied to the piezoelectric device to cause the motor, the turntableand the glass original plate to vibrate in the diameter direction of theglass original plate while the amplitude of variation was varied to be0.014×Q (mm) in accordance with the distance Q between the cutting headand the center of the glass original plate.

After the cutting was carried out in this way, development was carriedout to give a resist pattern in a spiral form with an elliptical shapeof 89.000 mm in length (a) of the minor axis and 89.623 mm in length (b)of the major axis, corresponding to a tracking groove having, at aconvex part, a width at the land, of 0.6 μm, a pitch of 1.6 μm and aheight of 1,000 Å. Next, this resist pattern was subjected to Nielectroforming to prepare a stamper. The resulting stamper was adheredwith an adhesive (trade name: SO-55; available from Sony Chemicals K.K.)to a roll substrate in the manner that the direction of the minor axisof the stamper was in accordance with the direction in which a resinsheet is transported. A roll stamper was thus produced.

Using this roll stamper, a plurality of preformats for optical diskswere transferred onto a polycarbonate resin sheet formed by extrusion,in the same manner as in Example 1. A substrate sheet for optical diskswas thus produced. With respect to the preformats on this substratesheet, measurement and evaluation were made in the same manner as inExample 1.

Results of the above Example 7 and 8 are shown in Table 6.

                                      TABLE 6                                     __________________________________________________________________________              Preformat pattern                                                                         Preformat on                                                                          Amount of                                                                           Amount of                                           on stamper                                                                             Sam-                                                                             resin sheet                                                                           deviation                                                                           ampltitude of                                       a    b   ple                                                                              a'  b'  from circle                                                                         tracking error                            Example:  (mm) (mm)                                                                              No.                                                                              (mm)                                                                              (mm)                                                                              (μm)                                                                             signals                                   __________________________________________________________________________    7         89.000                                                                             89.187                                                                            1  88.563                                                                            88.590                                                                            27    AA                                        (b - a/a) × 100 =                                                                          2  88.559                                                                            88.589                                                                            30    AA                                        0.21               3  88.611                                                                            88.641                                                                            30    AA                                        8         89.000                                                                             89.623                                                                            1  88.849                                                                            88.861                                                                            12    AA                                        (0.7)              2  88.842                                                                            88.857                                                                            15    AA                                                           3  88.854                                                                            88.865                                                                            11    AA                                        __________________________________________________________________________

Example 11

A flexible stamper having 9 preformat patterns as shown in FIG. 7A wasprepared.

This stamper was prepared as shown in FIG. 10 by spinner coating aphotoresist (trade name: AZ-1370, produced by Hoechst Japan) to athickness of 3000 Å on a glass substrate of 450 mm×450 mm×20 mm(thickness), followed by pre-baking under the conditions of 90° C., 30minutes.

Next, in the same manner as in Example 1, 9 resist patterns with a widthof 0.6 μm, a pitch of 1.6 μm and a depth of 1000 Å at the portioncorresponding to the track grooves shaped in ellipsoidal spiral with alength of shorter axis of a (89.222 mm) and a length of longer axis(width) of b (89.344 mm) were prepared.

As the pre-treatment for forming a metal film according to theelectroforming method, electroconducting treatment was carried out byuse of a sputtering apparatus to form a nickel film with a filmthickness of 1000 Å to 2000 Å, thereby forming an electroconducting film114 on a glass master.

Next, as shown in the same Figure (D), on the electroconducting film wasformed a nickel film 115 with a thickness of 100 to 200 μm according tothe electroforming method (step D).

The electroforming solution used here had a composition as shown below.

    ______________________________________                                        Nickel sulfamate.tetrahydrate                                                                       500     g/liter                                         [Ni(NH.sub.2 SO.sub.3).sub.2.4H.sub.2 O]                                      Boric acid [H.sub.3 BO.sub.3 ]                                                                      35-38   g/liter                                         Pit preventive        2.5     ml/liter.                                       ______________________________________                                    

Finally as shown in FIG. 10E, the electroconducting film and the metalfilm in one body are peeled at the same time from the glass master, andthe photoresist attached on the surface was removed to obtain a flexiblestamper with a size of 440 mm×400 mm as shown in FIG. 7A having formedpreformat patterns corresponding to the spiral-shaped guide grooves witha=89.222 mm, b=89.340 mm, line-and-space:1.6 μm/0.6 μm, stoppeddifference: 100 Å (step E). Two sheets of the flexible stamper thusobtained were screwed at both ends of the stamper 116 from above thefixing implements 153 as shown in FIG. 15B, and fixed on the rollsubstrate with a diameter of 300 mm so that the shorter axis of thepreformat pattern may coincide with the peripheral direction of the rollsubstrate to prepare a roll stamper.

Next, by use of the roll stamper, an apparatus for preparing a substratesheet for optical disc shown in FIG. 4 was prepared.

As shown in FIG. 4, a substrate sheet for an optical recording mediumwas prepared by use of an extrusion molding machine using a coat hangertype T-die with a 20 cm width set downwardly at the extruder 1 with ascrew diameter of 35 mm.

As the resin, a polycarbonate resin (trade name: Panlite L-1250;produced by Teijin Kasei) was employed. The pressure molding portion 49has mirror surface rolls for the rolls 41, 43, and the roll stamperprepared above for the roll 42.

A molten resin sheet was formed under the extrusion conditions of theresin sheet, namely at the barrel temperatures of the extruder 45 at thea portion (Ta) of 300° C., at the b portion (Tb)=300° C., the c portion(Tc)=320° C., and the temperature of the T-die 46 of Td=320° C. Theresin temperature at this time was 280° C. to 320° C.

The roll stamper 42 is maintained at 140° C., and the roll 41 wasmaintained at a temperature 1 to 2° C. lower than that of the roll 42,and the roll 43 at a temperature 20 to 21° C. higher than that of theroll 42.

The gap between the lip of the T-die and the pressure molding portionwas made 50 mm, and the atmosphere from extrusion of the resin sheet tothe pressure molding portion was controlled by enclosing therearoundwith a heating box so that it became 60° C. or higher. The lip openingof the T-die was made 1.5 mm and the gap between the rolls 41, 42 at thepressure molding portion 1.2 mm, under which conditions the preformatpatterns of the roll stamper 42 were transferred onto the resin sheet toprepare a substrate sheet for an optical disc with a thickness of 1.2mm.

The resin sheet was molded at a speed of 2 m/min. For the preformat onthe substrate sheet for the information recording medium thus formed,when the length in a direction parallel to the conveying direction ofthe resin sheet of the preformat is made a' and the length in thedirection vertical thereto b', the a' and b' are measured, and thedeviation of b' from a' taken as a standard is defined as the deviatedquantity from true sphere. The measured value is an average of 18samples obtained by molding of one rotation of the roll stamper. Theresults are shown in Table - 7.

                  TABLE 7                                                         ______________________________________                                                                Deviated Amplitude quantity                                                   quantity from                                                                          of tracking                                  Sample                                                                              a' (mm)  b' (mm)  true sphere                                                                            error signal                                 ______________________________________                                              88.688   88.684   4        ⊚                             ______________________________________                                    

Next, the substrate for an optical disc subjected to the abovemeasurement was cut off from the sheet, and then aluminum was vapordeposited to prepare an optical disc.

The optical disc was evaluated by an optical disc evaluation apparatus(trade name: OMS-1000, Type III; produced by Nakamichi K.K.), and theamplitude of tracking error signal was measured. However, at this time,the case when the amplitude was 0.2 V or less was shown by ⊚, the caseof 0.2 to 0.4 V by ◯, the case of 0.4 to 1.0 V by Δ, and the case whentracking is impossible by x.

Example 12

The stamper for optical disc shown in FIG. 7A was prepared according tothe method shown in FIG. 11. First, a photoresist layer was formed onthe base film 111 of a polyester with a thickness of 0.2 mm, a width of460 mm and a length of 3 m. For the photoresist, Az 1300* 4.6 cp(produced by Hoechst-Japan) was employed, which was coated by a basefilm coater to a film thickness of 1000 Å. Then, pre-baking was carriedout under the conditions of 90° C., 30 min.

Next, according to the same method as in Example 11, a resist patternfor optical disc was prepared.

Subsequently, the electroconducting film 114 to of nickel was formed onthe resist pattern a thickness of 1000 Å by sputtering. The base filmmaster was wound up in a roll and a nickel film was formed to athickness of 220 μm on the electroconducting film by use of anelectroforming apparatus shown in FIG. 13. The delivery speed of thebase film master was made 40 mm/min. Electrolysis was carried out by useof an electroforming solution of:

    ______________________________________                                        Nickel sulfamate.tetrahydrate                                                                       500     g/liter                                         [Ni(NH.sub.2 SO.sub.3).sub.2.4H.sub.2 O]                                      Boric acid [H.sub.3 BO.sub.3 ]                                                                      35-38   g/liter                                         Pit preventive        2.5     ml/liter.                                       ______________________________________                                    

under the conditions of 250 AH.

Next, the electroconducting film and the metal film were peeled from thebase film master to obtain a flexible stamper in continuous length.

The stamper was cut in conformity with a roll substrate of 300 mm indiameter, and adhered directly onto a stamper fixing implement 153 byuse of a cyanoacrylate type adhesive (trade name SC-55, Sony ChemicalK.K.) and fixed on the roll substrate so that the short axis directionof the preformat pattern may be consistent with the peripheral directionof the roll substrate, followed by fixing of the stamper fixingimplement having the flexible stamper fixed thereon by screwing onto theroll substrate to obtain a roll stamper having 18 preformat patterns.

By use of the roll stamper, a substrate sheet for an optical disc wasmolded in the same manner as in Example 11 by use of the roll stamper,and evaluated in the same manner as in Example 11.

The results of Example 12 as described above are shown in Table 8.

The predetermined preformat size of the optical discs in Example 1 to 12was made A=B=89.00 mm. That is B/A=1.

                  TABLE 8                                                         ______________________________________                                        Size of       Size of    Deviated  Amplitude                                  preformat     Preformat  amount    quantity of                                pattern       on resin   from true tracking                                   of stamper    sheet      sphere    error signal                               ______________________________________                                        Example                                                                              a      89.220  a'   88.689                                                                              1 μm ⊚                     12     b      89.340  b'   88.690                                             ______________________________________                                    

Example 13

A flexible stamper having 9 preformat patterns for an optical card asshown FIG. 7B was prepared.

So that a stripe-shaped groove with a width of 3 μm and a pitch of 12 μmwas formed in parallel to the widthwise direction on the substrate sheetfor an optical card within the region as a predetermined preformat ofoptical card with its length A of 30.990 mm and width B of 85.590 mm, asshown in FIG. 17, and also 2583 track groove patterns were formed withinthe region of the preformat pattern of the stamper with a length a of31.021 mm and a width b of 85.847 mm in parallel to the width direction.

The stamper was prepared as shown in FIG. 10A-D by spinner coating aphotoresist (trade name: Az-1370; produced by Hoechst Japan) on a glasssubstrate of 340 mm×340 mm×10 mm (thickness) to a thickness of 3000 Å,followed by pre-baking under the conditions of 90° C., 30 minutes.

Next, by use of a laser exposure apparatus (trade name: Mirror ProjectorMask Aligner·MPA-1500, produced by Canon), a 9 preformat patternscorresponding to the above size were exposed and developed by developerAx 312MIF (produced by Hoeschst Japan) to prepare a glass master 101having preformat patterns for optical card (step A).

Further, as shown in FIG. 10B, an electroconducting film 114 was formedon the glass master by effecting the electroconducting treatment by useof a sputtering device as the pre-treatment for forming the metal filmaccording to the electroplating method to form a nickel film with a filmthickness of 100 Å to 2000 Å.

Next, as shown in FIG. 10C, a nickel film 115 with a thickness of 100 to200 μm was formed according to the electroforming method.

The electroforming solution used here had a composition as shown below:

    ______________________________________                                        Nickel sulfamate.tetrahydrate                                                                       500     g/liter                                         [Ni(NH.sub.2 SO.sub.3).sub.2.4H.sub.2 O]                                      Boric acid [H.sub.3 BO.sub.3 ]                                                                      35-38   g/liter                                         Pit preventive        2.5     ml/liter.                                       ______________________________________                                    

Finally as shown in FIG. 10D, the electroconducting film and the metalfilm in one body are peeled at the same time from the glass master, andthe photoresist attached on the surface was removed to obtain a flexiblestamper with a size of 300 mm×300 mm as shown in FIG. 7B having formedunevenness corresponding to the spiral-shaped guide grooves withline-and-space: 9.5 μm/2.5 μm, stepped difference: 2500 Å to 3000 Å.

Three sheets of the flexible stamper thus obtained were screwed at theboth ends of the stamper 116 from above the fixing implements 153 asshown in FIG. 15B, and fixed on the roll substrate with a diameter of300 mm so that the length (a) direction of the preformat patterncoincide with the peripheral direction of the roll substrate to preparea roll stamper.

Next, by use of the roll stamper, an apparatus for preparing substratesheet for optical disc shown in FIG. 4 was prepared.

As shown in FIG. 4, a substrate sheet for optical recording medium wasprepared by use of an extrusion molding machine using a coat hanger typeT-die with a 20 cm width set downwardly at the extruder 1 with a screwdiameter of 35 mm.

As the resin, a polycarbonate resin (trade name: Penlite L-1250;produced by Teijin Kasei) was employed. The pressure molding portion 49has mirror surface rolls for the rolls 41, 43, and the roll stamperpreviously prepared for the roll 42.

A molten resin sheet was formed under the extrusion conditions of theresin sheet, namely at the barrel temperatures of the extruder 45 at thea portion (Ta) of 300° C., at the b portion (Tb)=300° C., the c portion(Tc)=320° C., and the temperature of the T-die 46 of Td=320° C. Theresin temperature at this time was 280° C. to 320° C.

The roll stamper 42 was maintained at 140° C., and the roll 41 wasmaintained at a temperature 1 to 2° C. lower than that of the roll 42,and the roll 43 at a temperature 20 to 21° C. higher than that of theroll 42.

The gap between the lip of the T-die and the pressure molding portionwas made 50 mm, and the atmosphere from extrusion of the resin sheet tothe pressure molding portion was controlled by enclosing it therearoundwith a heating box so that it became 60° C. or higher. The lip openingof the T-die was made 0.48 mm and the gap between the rolls 41, 42 atthe pressure molding portion 0.4 mm, under which conditions thepreformat patterns of the roll stamper 42 were transferred onto theresin sheet to prepare a substrate sheet for an optical disc with athickness of 0.4 mm.

The resin sheet was molded at a speed of 2 m/min. For the preformat onthe substrate sheet for the information recording medium thus formed,when the length in the direction parallel to the conveying direction ofthe resin sheet of said preformat is made a' and the length in thedirection vertical thereto b', the a' and b' were measured, and thedeviation of a' and b' from A and B, which are the predetermineddimension of the preformat pattern, taken as a standard is determined.

Example 14

A flexible stamper as shown in FIG. 7B was prepared according to themethod shown in FIG. 12.

A flexible stamper as shown in FIG. 7B was prepared according to themethod shown in FIG. 12.

First, a stamper made of nickel with a diameter of 86 mm (thickness 300μm) having stripe-shaped guide grooves with a line-and-space: 9.5 μm/2.5 μm, stepped difference: 2500 Å-3000 Å formed on a sheet of apolyester (Lumilar, produced by Toray) with a thickness of 10 μm, alength of 1000 mm and a width of 300 mm was backed with a chromium steelwith a thickness of 2 mm, sandwiched between similar chromium steels,and heated and pressurized by application of a pressure of 10 kg/cm² at200° C. for 2 minutes, to transfer the preformat pattern, therebypreparing a base film master.

Next, as shown in the same FIG. 12B, the electroconducting film 114 wasformed in the same manner as in Example 11, and then the metal film 115was formed.

Next, the base film master in this state was wound up in a roll, and anickel film was formed to a thickness of 220 μm on the electroconductingfilm by use of the electroforming apparatus shown in FIG. 13. Thedelivery speed of the base film at this time was made 40 mm/min., andthe electrolytic condition 250 AH.

Subsequently, the electroconducting film and the metal film were peeledfrom the base film master to obtain a flexible pattern in a continuouslength shown in FIG. 18. The stamper was cut in conformity with a rollwith a diameter of 300 mm to form a flexible stamper having 6 preformatpatterns with strip-shaped track grooves having a length a=31.036 mm, awidth b=85.932 mm, a line-and-space of 9.5 μm/2.5 μm and a groove depthof 2500 Å to 3000 Å.

Next, the stamper was fixed by screwing of both ends thereof from abovethe stamper fixing implement 3 as shown in FIG. 15C so that the length(a) direction of the preformat pattern was consistent with theperipheral direction of the roll substrate to prepare a roll stamper.

By use of the roll stamper, a substrate sheet for optical card wasprepared in the same manner as in Example 13 and evaluated.

Example 15

A flexible stamper for optical card as shown in FIG. 7B was preparedaccording to the electroforming method.

First, as shown in FIG. 16A, an electroconducting film 114 was formed ona polyester base film 111 by sputtering as the pre-treatment forformation of a metal film 115 according to the electroforming method.

Here, by forming a nickel film with a film thickness of 1000 to 2000 Å,the electroconducting film 114 was formed on the base film 111.

Next, as shown in the same FIG. 16B, the metal film 115 was formed onthe electroconducting film according to the electroforming method.

First, as shown in FIG. 13, the nickel chip 132 within theelectroforming tank was set on the + side electrode and the base filmprovided with the electroconducting film on the - side, and the basefilm was continuously delivered into the electroforming solution.

While moving the base film provided with the electroconducting film 9 ina nickel sulfamate solution in the arrowhead direction in FIG. 2, nickelmetal of 100 to 200 μm was deposited under the conditions of timeintegrated values 17 to 34 AH (apere·hour) of the passed current to forma metal film 115.

The electroforming solution used here had the following composition:

    ______________________________________                                        Nickel sulfamate.tetrahydrate                                                                       500     g/liter                                         [Ni(NH.sub.2 SO.sub.3).sub.2.4H.sub.2 O]                                      Boric acid [H.sub.3 BO.sub.3 ]                                                                      35-38   g/liter                                         Pit preventive        2.5     ml/liter.                                       ______________________________________                                    

Next, after the surface of the metal film 115 was polished, aphotoresist was coated thereon, followed by exposure and developing toform a resist pattern.

The polishing method may be carried out according to the 2 steps of drypolishing and wet polishing, and in dry polishing, polishing was carriedout by use of MC diamond disc #230 (trade name) for the polishing clothfor 8 hours, while in wet polishing, polishing was carried out by use ofSuede 7355-000F42S (trade name) for the polishing cloth and POLIPLA700(trade name) for the polishing agent for 16 hours. The extent ofpolishing was made within ±3 Newton rings for the surface precision, and50 to 100 angstroms or less for the surface roughness.

Here, as the photoresist, Az1370 (produced by Hoechst-Japan) wasemployed and this was coated on the polished metal film 13 to a filmthickness of 3000 Å by a roll coater. Then, pre-baking was carried outunder the conditions of 90° C., 30 min. Next, by means of a laserexposure apparatus, Mirror Projector Mask Aligner·MPA-1500 (produced byCanon), the preformat pattern (stripe shape) was exposed and developedby a developer Az312MIF (produced by Hoechst-Japan), followed bypost-baking to form a resist pattern.

Finally, the metal film 115 was subjected to wet etching. The wetetching was carried out by effecting etching with a solution ofhydrofluoric acid and ammonia fluoride NH4F (1:7 weight ratio) for about1 minute, while rotating the metal film (electroformedfilm+electroconducting film+film) around its own axis.

After etching, O₂ plasma etching was applied by use of O₂, and theresidual resist was removed, whereby a fine pattern corresponding to thepatterning-pattern was formed on the metal film.

Thus, a flexible stamper in a continuous length shown in FIG. 18 havinga stripe-shaped preformat pattern with a=31.005 mm, b=85.676 mm and aline-and-space: 9.5 μm/2.5 μm, stepped difference: 2500-3000 Å, wasobtained. Subsequently, the stamper was cut in conformity with a rollsubstrate with a diameter of 300 mm, fixed in the same manner as inExample 14 so that the length a direction may be consistent with theperipheral direction of the roll stamper, and molding of the substratesheet for optical card was carried out.

For Examples 13 to 15 as described above, dimensional deviations of therespective values a' and b' from A, B were measured to obtain theresults shown in Table 9.

Reference examples 1, 2

As reference examples, in the same manner is in Example 13 except forchanging the dimensions a, b of the preformat pattern to the sizes shownin Table 9, the preformat pattern was transferred. The results are shownin Table 9.

                                      TABLE 9                                     __________________________________________________________________________                                        Deviated amount                                                               from the                                                    Size of preformat predetermined                                               pattern of                                                                             Size of preformat                                                                      preformat size                                              stamper  on resin sheet                                                                         (A × B)                             __________________________________________________________________________    Example 13                                                                                ##STR1##                                                                            a  31.021 mm                                                                           a' 30.989 mm                                                                            1 μm                                              ##STR2##                                                                            b  85.847 mm                                                                           b' 85.592 mm                                                                            2 μm                                  Example 14 (0.15) a  31.036                                                                              a' 31.005                                                                               15 μm                                            (0.4)  b  85.932                                                                              b' 85.676                                                                               86 μm                                 Example 15 (0.05) a  31.005                                                                              a' 30.975                                                                               15 μm                                            (0.1)  b  85.676                                                                              b' 85.419                                                                              171 μm                                 Reference example 1                                                                      (0.01) a  30.993                                                                              a' 30.962                                                                               28 μm                                            (0.05) b  85.632                                                                              b' 85.376                                                                              214 μm                                 Reference example 2                                                                      (0.3)  a  31.082                                                                              a' 31.052                                                                               62 μm                                            (0.7)  b  86.189                                                                              b' 85.932                                                                              342 μ m                                __________________________________________________________________________

We claim:
 1. A roll stamper having an axis and having on its peripheralsurface a preformat pattern corresponding to a preformat of aninformation recording disc having a circular or spiral trackinggroove,wherein said roller stamper is adapted to transfer the preformatpattern onto a melt-extruded resin sheet in succession to mold the resinsheet into the information recording disc, wherein the preformat patterncorresponding to the circular or spiral tracking groove has anelliptical form having a minor axis in a rotation direction of the rollstamper and a major axis in a direction parallel to the axis of the rollstamper.
 2. A roll stamper according to claim 1, wherein a and b satisfythe following relationship:

    0.05≦(b-a)/a×100≦2

wherein a and b are defined, respectively, as the length of the minorand major axes of the elliptical form at the outermost periphery of thepattern corresponding to the circular or spiral tracking groove.
 3. Aroll stamper according to claim 2, wherein the diameters a and bsatisfy:

    0.1≦(b-a)/a×100≦1.


4. A roll stamper having an axis and having on its peripheral surface aplurality of preformat patterns corresponding to a preformat of aninformation recording disc having a circular or spiral trackinggroove,wherein the preformat pattern corresponding to the circular orspiral tracking groove has an elliptical form having a minor axis in arotation direction of the roll stamper and a major axis in a directionparallel to the axis of the roll stamper.
 5. A roll stamper according toclaim 4, wherein a and b satisfy the following relationship:

    0.05≦(b-a)/a×100≦2,

wherein a and b are defined, respectively, as the length of the minorand major axes of the elliptical form at the outermost periphery of thepattern corresponding to the circular or spiral tracking groove.
 6. Aroll stamper according to claim 5, wherein the diameters a and bsatisfy:

    0.01≦(b-a)a×100≦1.


7. A roll stamper according to claim 4, wherein the roll stamper has aroll substrate and a flexible stamper fixed on the surface of said rollsubstrate, and wherein on the surface of said flexible stamper is formedsaid plurality of the preformat patterns in the peripheral direction ofsaid roll substrate.
 8. A roll stamper according to claim 7, furthercomprising means for fixing the flexible stamper.
 9. A roll stamperaccording to claim 8, wherein said fixing means comprises a stamperfixing implement for holding said flexible stamper sandwiched betweensaid stamper fixing implement and said roll substrate and means forfixing said stamper fixing implement onto said roll substrate.
 10. Aroll stamper having an axis and having on its peripheral surface apreformat pattern corresponding to a preformat of an informationrecording disc having a circular or spiral tracking groove,wherein thepreformat pattern corresponding to the circular or spiral trackinggroove has an elliptical form having a minor axis in a rotationdirection of the roll stamper and a major axis in a direction parallelto the axis of the roller stamper.